In prior arts, Japanese Patent Examined Application Publication No. 57-54068 etc. proposes a surface protection sheet for protecting a surface of a metal plate. The surface protection sheet is applied to prevent the metal surface from being damaged by scratches in processing, transporting or stacking the metal plate.
These surface protection sheets are used when bending metal plates mainly, intending to prevent an occurrence of scratches on the metal plates due to contacts between a bending die and the metal plates at processing. Further, when a punch press is used in a process preceding the bending process, there is a possibility that a punching chip remaining in a lower metal mold (die) after completing the punching process rises with an elevation of an upper metal mold (punch) for the punch press, runs on a surface of the metal plate or enters between the work subject material and the die. In this case, the surface (upper or lower surface) of the metal plate is damaged (scratches etc.) since the upper metal mold bears down the punching chip at a sequent punching process (note, this phenomenon will be referred to as “chip-up phenomenon” hereinafter).
In case of punching a metal plate equipped with this surface protection sheet, the chip-up phenomenon becomes remarkable because there is a possibility that the surface protection sheet is not cut off to cause a punching chip or the protection sheet itself to run on the surface of the metal plate. In order to solve the above chip-up phenomenon, there are proposed dies intending to prevent an occurrence of the chip-up phenomenon, in Japanese Utility Model Examined application Publication No. 52-50475, Japanese Patent Application Laid-open No. 2000-51966, Japanese Patent Application Laid-open No. 2004-1055 and Japanese Patent Application Laid-open No. 2004-17113. With the use of the dies proposed in these publications, it is possible to suppress the occurrence of chip-up phenomenon. Depending on the variety of surface protection sheets, however, there also exists a die that is almost ineffective in reducing the chip-up phenomenon.
In order to prevent an occurrence of scratches on the surfaces of metal plates in stacking or transporting them after punching, additionally, there is also devised a countermeasure where it is not performed at punching to apply the surface protection sheet accounting for the chip-up phenomenon onto the surface of the metal plate, but instead performed at stacking a punched metal plate to firstly apply a surface protection sheet on a previously-punched metal plate and secondly stack the presently-punched metal plate on the surface protection sheet. However, this countermeasure is accompanied with considerably-troublesome task because this attaching operation of the surface protection sheet is normally performed by worker's hands manually.